From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8A270340A57; Wed, 20 May 2026 18:23:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779301434; cv=none; b=TlUX/mXv/vfHaV9mhkZ0iYgqa1pnJdl4nkIQmfBPFM62MEptnwTYw6U7W/ag7azwfcjxoNloKQUObenO8bgpEiLVF5WmbuwP8Pc59fJgkaXwY2+JSNE2X4eguBKKzjJcp8Ed1EbV6/QDiyyTc/w+a8AbjOA1XEWFJ8Wh96Y2k3o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779301434; c=relaxed/simple; bh=HAWEUq9CUTpIq+MJODGb9xWGAlUMamk0LOdR5h7Umwo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mb4SM+96Q+WzsDqiY/MINpMqIOHE6BfNnfRUvINLT1DXfYag5FBWJeiZ+x8AHfP5tLIKnJVr4icDJwpgesgxwOofctPHJbQ6ytpEr6kl6UaBANNckiQVw3ucMLhFmbQx0fZY35ICWIV5Pvsc/qrf4u66cjvQ9Dz9DqxWwhL+pzQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=M3p94DyE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="M3p94DyE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F07111F000E9; Wed, 20 May 2026 18:23:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779301433; bh=r3NtgaRdk+3QeBe/OJoiOrqxesDQGikR0zIYF3wW2w0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=M3p94DyEL/5sbTUJyXHEtvUWv+RUlnkY3cVXe6IC9EKnseBKQb6zWYeZ96tdAV7Dq qJ0lBY5SdCmzQNfh6Zvbqqj1ZVBgN4E+JUBrS+ir6JuyPj0qcn60a5lDs2zBygRObt HrlydeafwxEzbzeNAxUKhn+JOnhaTgb1VAdjYC8w= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Zicheng Qu , "Peter Zijlstra (Intel)" , Sasha Levin , Hui Tang , Zhang Qiao Subject: [PATCH 6.12 552/666] sched/fair: Clear rel_deadline when initializing forked entities Date: Wed, 20 May 2026 18:22:43 +0200 Message-ID: <20260520162123.231125804@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162111.222830634@linuxfoundation.org> References: <20260520162111.222830634@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zicheng Qu [ Upstream commit 3da56dc063cd77b9c0b40add930767fab4e389f3 ] A yield-triggered crash can happen when a newly forked sched_entity enters the fair class with se->rel_deadline unexpectedly set. The failing sequence is: 1. A task is forked while se->rel_deadline is still set. 2. __sched_fork() initializes vruntime, vlag and other sched_entity state, but does not clear rel_deadline. 3. On the first enqueue, enqueue_entity() calls place_entity(). 4. Because se->rel_deadline is set, place_entity() treats se->deadline as a relative deadline and converts it to an absolute deadline by adding the current vruntime. 5. However, the forked entity's deadline is not a valid inherited relative deadline for this new scheduling instance, so the conversion produces an abnormally large deadline. 6. If the task later calls sched_yield(), yield_task_fair() advances se->vruntime to se->deadline. 7. The inflated vruntime is then used by the following enqueue path, where the vruntime-derived key can overflow when multiplied by the entity weight. 8. This corrupts cfs_rq->sum_w_vruntime, breaks EEVDF eligibility calculation, and can eventually make all entities appear ineligible. pick_next_entity() may then return NULL unexpectedly, leading to a later NULL dereference. A captured trace shows the effect clearly. Before yield, the entity's vruntime was around: 9834017729983308 After yield_task_fair() executed: se->vruntime = se->deadline the vruntime jumped to: 19668035460670230 and the deadline was later advanced further to: 19668035463470230 This shows that the deadline had already become abnormally large before yield_task_fair() copied it into vruntime. rel_deadline is only meaningful when se->deadline really carries a relative deadline that still needs to be placed against vruntime. A freshly forked sched_entity should not inherit or retain this state. Clear se->rel_deadline in __sched_fork(), together with the other sched_entity runtime state, so that the first enqueue does not interpret the new entity's deadline as a stale relative deadline. Fixes: 82e9d0456e06 ("sched/fair: Avoid re-setting virtual deadline on 'migrations'") Analyzed-by: Hui Tang Analyzed-by: Zhang Qiao Signed-off-by: Zicheng Qu Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260424071113.1199600-1-quzicheng@huawei.com Signed-off-by: Sasha Levin --- kernel/sched/core.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index df76b32a013fb..9b238c9c71c67 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4453,6 +4453,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p) p->se.nr_migrations = 0; p->se.vruntime = 0; p->se.vlag = 0; + p->se.rel_deadline = 0; INIT_LIST_HEAD(&p->se.group_node); /* A delayed task cannot be in clone(). */ -- 2.53.0